How to open a serial port by friendly name?

Question

friendly name = the name that appears in \"Device Manager\" under \"Ports (COM & LPT).

EDIT: two solutions provided below. One with WMI and another with SetupAPI

Answer 1

Pavel's class SetupDiWrap works great, it just needs a few small tweaks for Windows 7.

Hopefully, this update will help other people struggling (like me) to get COM port numbers from VCP names in Windows 7.

1) The SP_DEVINFO_DATA has changed in Windows 7, the total length is no longer 28 bytes, it is 32 bytes long. This is what works for me:

   private struct SP_DEVINFO_DATA
        {
            /// 
Size of the structure, in bytes.
            public int cbSize;
            /// 
GUID of the device interface class.
            public Guid ClassGuid;
            /// 
Handle to this device instance.
            public int DevInst;
            /// 
Reserved; do not use.
            public ulong Reserved;
        }

Note ulong for Reserved instead of an int. Changing uint cbSize to int cbSize saved me a cast later on, otherwise you can leave it as uint.

2) I also wrote the line:

 da.cbSize = (uint)Marshal.SizeOf(da);

a bit different, for clarity, to get the cbSize to 32 bits:

da.cbSize = Marshal.SizeOf(typeof(SP_DEVINFO_DATA));

3) I changed

 [DllImport("setupapi.dll", CharSet = CharSet.Auto)]
        static extern IntPtr SetupDiGetClassDevs(       
           ref Guid ClassGuid,
           IntPtr Enumerator,
           IntPtr hwndParent,
           int Flags
        );

to

 [DllImport("setupapi.dll", CharSet = CharSet.Auto)]
        private static extern IntPtr SetupDiGetClassDevs( 
           ref Guid ClassGuid,
           UInt32 Enumerator,
           IntPtr hwndParent,
           UInt32 Flags
        );

The Enumerator is no longer an IntPtr, so you need to call SetupDiGetClassDevs like this:

IntPtr h = SetupDiGetClassDevs(ref guidClone, 0, IntPtr.Zero, DIGCF_PRESENT | DIGCF_PROFILE);

Note "0" instead of IntPtr.Zero when passing the Enumerator.

The code now runs like a charm in Windows 7!